1. Field of the Invention
The present invention relates to an electric operation apparatus, or more particularly, to an electric operation apparatus characterized by an output control unit with which high-frequency current is conducted.
2. Description of the Related Art
In general, an electric operation apparatus including an electric cautery is used to incise or coagulate a living tissue or arrest bleeding from a living tissue in the course of a surgical or an internal operation for remedying a bodily injury or a disease or dysfunction.
This kind of electric operation apparatus consists mainly of a diathermic power supply and an electrode that serves as a therapeutic accessory (operating instrument) and is connected to the diathermic power supply. In the electric operation apparatus, the electrode is brought into contact with a patient's living tissue, and high-frequency output power is delivered from the diathermic power supply. Consequently, the patient's living tissue is remedied with high-frequency current conducted with the output power.
When the electric operation apparatus is used to deliver high-frequency output power to a living tissue, the living tissue is heated with high-frequency current conducted with the output power. Consequently, the living tissue is denatured, and then has water thereof depleted. Eventually, the living tissue dries up. The living tissue is coagulated in due course. Although the living tissue gets dried up, if high-frequency output power is kept delivered, the living tissue is carbonized to adhere to the electrode. In order to prevent a living tissue from adhering to the electrode, when the living tissue gets dried up, delivery of high-frequency output power must be stopped.
In the conventional electric operation apparatus, when high-frequency output power of a constant level shown in FIG. 18A is delivered to a living tissue irrespective of passage of time, the living tissue is denatured and dried up. Consequently, the temperature exhibited by the living tissue gradually rises as shown in FIG. 18B. On the other hand, as shown in FIG. 18C, the impedance offered by the living tissue decreases in an early stage, remains nearly constant for some time, and then abruptly rises along with the dry of the living tissue. Therefore, as far as the conventional electric operation apparatus is concerned, as soon as it is judged from the impedance or temperature of a living tissue that the living tissue is dried up, delivery of high-frequency output power is stopped or any other control sequence is performed.
Various proposals have been made of the foregoing electric operation apparatus in the past. For example, U.S. Pat. No. 5,540,684 has proposed an electric operation apparatus that judges from the impedance offered by a living tissue whether the living tissue has been coagulated, and stops delivery of high-frequency output power when the living tissue has been coagulated. Thus, carbonization of a coagulated living tissue is prevented and adhesion of the living tissue to an electrode is avoided.
Moreover, the present applicant has filed Japanese Patent Unexamined Publication No. 10-225462 and proposed an electric operation apparatus that lowers high-frequency output power so as to accomplish the same object as the U.S. Pat. No. 5,540,684.
In the electric operation apparatuses described in the Japanese Patent Unexamined Publication No. 10-225462 and the U.S. Pat. No. 5,540,684, when a living tissue to be coagulated has a very large volume, output power with which high-frequency current is conducted must be raised in order to exert a satisfactory coagulation ability. For this reason, the electric operation apparatuses have difficulty in preventing carbonization of a living tissue and avoiding adhesion of the living tissue to an electrode.